Increasing interest in protecting the environment has resulted in heightened concerns about the pollution and other dangers resulting from leakage from underground storage tanks for hazardous liquids. Some of these concerns include the problem of leakage of the liquid into ground water supplies and dangers due to fires or explosions. Many of these storage tanks were placed underground in the 1950s and 1960s as a fire prevention measure in order to reduce the risk of damage from stored flammable liquids such as gasoline. Such tanks are often constructed from bare steel, are not protected from corrosion and have now reached or are nearing the end of their useful lives. It has been estimated that as many as 400,000 of these underground storage tanks are now leaking and that many more will begin leaking in the near future.
In an attempt to correct this problem in the United States, the U.S. Environmental Protection Agency (EPA) issued strict regulations at the end of 1988 which mandate certain duties and responsibilities on the part of owners of underground storage tanks including burdensome and expensive corrective action that these owners must take. It will be appreciated that, even apart from the burdens of the EPA regulations, if a leak in a tank is detected, the basic options are limited and burdensome to an owner, i.e., the tank can be drained and abandoned, dug out of the ground and repaired or discarded, or repaired while in the ground, all of which are expensive operations. As the deadline for compliance imposed by the EPA regulations approaches, owners of underground tanks have been considering more and more the alternative of aboveground storage. However, while constructing aboveground storage tanks largely eliminates the need to comply with strict environmental regulations, these regulations are replaced by the vagaries of state and local safety codes. For example, many of the codes require that the inner tank be listed by Underwriter's Laboratory (UL), that secondary containment be provided, and that flammable liquids have a two hour fire wall at 2,000 degrees F. It should be noted that simple aboveground tanks alone are clearly prohibited and that storage "vaults," i.e., tanks within an outer containment, are required. In general, a UL inner tank encased within six inches of concrete will be designated as a vault and will meet most state and local safety codes while being exempted from current Federal regulations.
Some recently developed vault technology involves the use of a custom fabricated rectangular steel tank encased or entombed within a block of standard concrete. An example of such a vault apparatus is that disclosed in U.S. Pat. No. 4,826,644 (Linguist et al) wherein an inner tank is entombed within a concrete outer tank using a specialized method.
A further patent possible interest in U.S. Pat. No. 4,895,272 (DeBenedittis et al.) which relates to a liquid storage system including an external containment vessel which is open on top and an internal storage tank disposed within the external containment vessel so as to define an outer storage space therein. A drainage arrangement provides coupling of liquid from a vent on the internal storage tank to the outer storage space.